Drive-slip control device for motor vehicles

ABSTRACT

A Drive-slip control device for motor vehicles in which, when a driven vehicle wheel spins, this wheel is braked and wherein when both driven wheels spin, the engine power is additionally reduced. Spinning of the drive wheels is recognized by means of rotational-speed sensors and an electronic system and when a spin signal is present on account of a differential-speed threshold value between driven and non-driven vehicle axles being exceeded, the power of the engine is reduced in a controlled manner by the electronic system during the duration of the spin signal by means of a final control element. When the spin signal stops, the power of the engine is increased again in a controlled manner to the target value predetermined by the driver by means of the accelerator. However, when power is reduced by the driver during a control operation of the drive-slip control device, below the engine control target value predetermined by the electronic system of the drive-slip control device (during a gear shift) and when power is increased again (when the gear-shift operation is complete) provided this takes place within a predetermined time, only the value which was also present before the reduction of power is permitted again as maximum power.

BACKGROUND AND SUMMARY OF THE INVENTION

The invention relates to a drive-slip control device for motor vehiclesin which, when a driven vehicle wheel spins, this wheel is braked andwhen both driven wheels spin, engine power is also reduced. Spinning ofthe drive wheels is recognized by means of rotational-speed sensors andan electronic system and, when a spin signal is present on account of adifferential-speed threshold value between driven and non-driven vehicleaxle being exceeded, the power of the engine is reduced in a controlledmanner by the electronic system during the duration of the spin signalby means of a final control element. When the spin signal ceases, thepower of the engine is increased again in a controlled manner to atarget value predetermined by the driver by means of the accelerator.

A drive-slip control device of this general nature can be found (GermanOffenLegungsschrift 3,544,294)the object of which is generally toprevent uncontrolled spinning of the drive wheels when a vehicle isbeing started on a smooth base.

The spinning of the wheels is sensed by wheel rotational-speed sensorsand is evaluated in the electronic system. If only one wheel spins, theassociated wheel brake is actuated (differential brake) via a brakecontrol valve. A drive moment is thereby transmitted via the wheeldifferential to the other non-slipping wheel.

If both drive wheels spin, however, the power of the driving engine isreduced in a controlled manner. To this end, the throttle linkage isoperated to reduce the value set by the driver.

The engine control by the drive-slip control device thus normally comesinto effect when there is a certain differential speed between thedriven and non-driven vehicle axles. If the speed again drops below thisspeed differential threshold, the engine over-ride control is switchedoff and the power of the engine is again increased in a controlledmanner to the value predetermined by the driver via the acceleratorpedal.

During gear-shift operations in particular, when the engine control bythe drive-slip control device works before gear disengagement, it isfound that after the reengagement and acceleration, the known enginecontrol function of the drive-slip control device is not always able toabsorb the excess power occurring. Correspondingly, high slip amplitudescan occur and thus lead to instability of the vehicle. This appliesequally when power is reduced by easing back on the accelerator and whenthe throttle is again opened immediately afterwards and without agear-shift operation. This corresponds, to a shock reaction or a speedadaption.

The object of the invention is to design a drive-slip control device ofthe above general nature in such a way that the travelling stability ofthe vehicle is also ensured during gear shift operations as mentionedabove.

This object is achieved when the predetermined driver accelerator targetvalue falls back during an engine control operation of the drive-slipcontrol device to or below the instantaneous control target valuereached at an instant during the control operation because of a gearshift. This instantaneous control target value reached at that instantis recorded and is used for the final controlling control element. Theinstantaneous control target value also corresponds to the instantaneousaccelerator target value at that instant. The recorded instantaneouscontrol target value is stored for a predetermined time. After the powerfalls back during reacceleration after the gear shift, the controloperation to increase power (by the presetting of a new acceleratortarget value) follows the accelerator target value only when the storedinstantaneous control target value is reached after a predetermined timeperiod, whereas it follows the engine-control target value trend whenthe stored instantaneous control target value is reached within thepredetermined time period.

The invention here starts from the consideration that the transmittablepower, e.g. before and after a gearshift operation is about the same,when the condition of the roadway remains stable, so that the value formaximum power after a gear-shift operation should be that value whichwas present before the gear-shift operation after an engine controloperation of the drive-slip control device.

Other objects, advantages and novel features of the present inventionwill become apparent from the following detailed description of theinvention when considered in conjunction with the accompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 shows a schematic block diagram of the drive-slip control device,

FIG. 2 shows vehicle characteristic diagrams,

FIG. 3 shows a diagram explaining the invention, and

FIG. 4 shows a sequence diagram.

DETAILED DESCRIPTION OF THE DRAWINGS

According to the FIG. 1, wheel rotational-speed signals n_(VL) andn_(VR) from the non-driven wheels and n_(HL) and n_(HR) from the drivenwheels are fed by rotational-speed sensors 4.1 to 4.4 to a signalprocessing stage 3 of the electronic control system 2 of the drive-slipcontrol device 1 and are converted by signal processing stage 3 intowheel speed signals v_(VL), v_(VR), v_(HL), and v_(HR) which in turn arefed to a comparator circuit 5. The comparator circuit is utilized todetermine whether both drive wheels are slipping, as well as averagespeeds v_(v) and v_(H) of the non-driven and driven axle, which arecompared to one another. It is possible to treat v_(v) as equivalent tovehicle travelling speed. If v_(H) relative to v_(v), now exceeds apredetermined target value Δv (for example 1.8 km/h) a spin signal S isproduced which is fed to a module 8 of the drive-slip control devicewhich generates a corresponding engine-control target value S_(A) andapplies it via a memory device 9 to a final control element 6.1 of athrottle valve control system 6 (or fuel injection pump). This signalS_(A) has priority over the driver accelerator target value signal f,Likewise fed via the memory 9, so that direct control of the engine bythe driver is prevented. The signal S_(A) now causes the engine power tobe reduced in a controlled manner during the duration of the signal S.The duration of the signal S depends on when, on account of the calledfor reduction in power S_(A), v_(H) relative to v_(v) again falls belowthe predetermined threshold target value Δv. If v_(H) falls below thispredetermined threshold value Δv, the signal S is eliminated and thepower of the engine is again increased in a controlled manner to theaccelerator target value f predetermined by the driver, unless thethreshold value is again exceeded and a new spin signal S is generated.This operation can be repeated several times, as shown in FIG. 2 withreference to the signals S₁ to S₃.

Referring to FIG. 3, if a reduction in power is now made during anengine-control operation I of the drive-slip control device (for examplea gear shift takes place), the accelerator target value f, during thereturn movement of the driver accelerator 7, follows the broken linecharacteristic curve f of FIG. 3. At the instant t, the instantaneousaccelerator target value corresponds to the instantaneous control targetvalue reached during the control operation of the drive-slip controldevice of the engine-control target value (solid line S_(A)). Thisinstantaneous control target value S_(At) at the point of the overlapf/S_(A) is now stored in the memory 9, for a predetermined time t_(SP)(e.g. 3.4 seconds). During gear-shift operation II, the acceleratortarget value f falls back still further and, once the shift operation iscomplete, again rises during acceleration by being increased by theaccelerator 7. If the accelerator target value f reaches the storedinstantaneous control target value S_(At) within the predetermined timet_(SP), the further control operation III takes place according to theengine-control target value S_(A). If, on the other hand, theinstantaneous control target value S_(At) is only reached after passageof the storage time t_(SP), the further control operation to increasepower takes place according to the accelerator target value f. Thusduring the time period t_(SP), the value S_(At) controls and only afterpassage of the time period t_(SP) can the then current setting of fcontrol.

The sequence logic required for the memory 9 is shown in FIG. 4.Initially the values f and S_(A) are read at out a box 7 and compared atbox 8. If f is equal to or less than S_(A), S_(A) is stored at box 9. Iff is greater than S_(A), slip occurs and an engine control (throttle,fuel, ignition, etc.) is caused to happen by box 10 which will also feedback to control S_(A) at box 7. At such time as value f becomes equal toor lower than S_(A), the stored value of S_(A) from the control at box11 (box 9 is during the time period t_(SP) at box 12) as long as f isless than the value stored at box 8 and this signal goes to box 11. If fis greater then that at box 13, this causes f to be the input to box 11and it is then transmitted to box 12. Until the time period t_(SP)passes, box 12 causes the stored S_(At) signal to control and afterpassage of t_(SP) allows f to control if f is fed to box 11, or elseS_(A) continues to control via box 14.

As is further apparent from FIG. 1, a signal for controlling the wheelbrake BR is also produced by the comparator circuit 5 when slipping of adrive wheel on one side is recognized.

Although means of influencing the engine power by taking action on thethrottle-valve control system is described in the exemplary embodiment,it is of course also possible to take action of way of controlling theengine ignition, or the fuel supply.

Although the present invention has been described and illustrated indetail, it is to be clearly understood that the same is by way ofillustration and example only, and is not to be taken by way oflimitation. The spirit and scope of the present invention are to belimited only by the terms of the appended claims.

We claim:
 1. Drive-slip control apparatus for a motor vehicle havingdriven and non-driven wheels, and engine and an accelerator,comprising:Sensor means for measuring separately rotational speed ofeach of said driven and non-driven wheels; Spin signal generating means,responsive to output signals from said sensor means, for detecting adifference between the rotational speed of said driven and saidnon-driven wheels, and for generating a spin signal when said differenceexceeds a predetermined threshold value; Drive-Slip control means forgenerating an engine control target signal in response to said spinsignal; Engine control means for reducing and increasing power of saidengine in a controlled manner in response to said engine control targetsignal; Accelerator target control means for generating an acceleratortarget signal in response to a position of said accelerator pedal;Memory means for detecting and storing, for a predetermined timeinterval, an instantaneous value of said engine control target signal,whenever said accelerator target signal equals or falls below saidengine control target signal; Said engine control means being adapted tocause speed of said engine to increase in response to said enginecontrol target signal if said accelerator target signal thereafterincreases to a value equal to or exceeding said stored instantaneousvalue of said engine control target signal within said predeterminedtime interval, and otherwise to cause the speed of said engine toincrease in response to said accelerator target signal.
 2. Apparatusaccording to claim 1, wherein said spin signal generating means isfurther adapted to detect a difference in the rotational speed asbetween one of said driven wheels and at least one other of said drivenwheels, and to cause application of a breaking force to one of saiddriven wheels in response thereto.